Landing gear strut extender

ABSTRACT

A mechanism for increasing the ride height of aircraft by selectively increasing the hydraulic fluid content within landing gear struts. By increasing the hydraulic fluid volume within a strut, the strut is lengthened without adversely affecting its spring rate while the ability to withdraw fluid from a strut maintains the ability of the strut to absorb the impact of landing. The mechanism is readily retrofitable to existing landing gear systems to accommodate more efficient under the wing intake designs and to reduce the likelihood of FOD during taxiing at minimal cost and with very a minimal increase in the aircraft weight.

BACKGROUND OF THE INVENTION

The present invention generally relates to aircraft landing gear andmore particularly pertains to landing gear with adjustable ride height.

In the design of an aircraft having engines mounted under the wing, thelanding gear must be sufficiently long in order to provide adequateengine ground clearance. Additional length allows the engine inlets tobe designed for more economical operation in flight (i.e. less drag) andthe engines themselves would be less prone to damage during on-groundoperations due to the ingestion of FOD (Foreign Object Damage). However,a longer landing gear adds considerable weight and some expense to theaircraft. This is particularly true when modifying an existing aircraftdesign to stretch the fuselage or add larger diameter engines, etc.,because revising an existing landing gear configuration in order to gainlength would be extremely expensive as well as add considerable weight.

It is therefore desirable to be able to temporarily lengthen a landinggear for purposes such as liftoff rotation or engine ground clearancewithout actually making the landing gear itself larger or heavier.Additionally, it would desirable to be able to temporarily lengthen thelanding gear without adversely affecting its spring rate.

SUMMARY OF THE INVENTION

Large aircraft landing gear structures typically employ a shock strut orequivalent means that is fully extended when the aircraft is in flight,and which compresses approximately 18 to 24 inches when the aircraft ison the ground. These shock struts typically contain pressurized oil toflow through orifices for shock absorbing and compressed gas to supportthe aircraft weight and provide the equivalent of a “suspension spring”for ride quality. When taxiing on the ground, the aircraft weight in theabsence of aerodynamic lift compresses the struts such that they arenearly fully compressed.

In one presently preferred embodiment of the invention a fluid pump,reservoir, and control valves are connected to the portion of the strutthat contains the oil (typically the “lower strut servicing port”) withwhich oil is pumped into or out of the strut, depending upon whether itis desirable to inject fluid into the strut to lengthen it for on-groundoperations or remove oil from the strut in preparation for absorbing thelanding impact energy.

Injecting fluid into the strut: Normally, when taxiing on the ground thelanding gear strut is nearly fully compressed by the aircraft weightthat it is supporting. An apparatus according to the present inventionwould inject fluid into the strut after landing as the full weight ofthis aircraft is supported by the struts. Adding fluid to the strutcauses the strut to extend, but does not change the volume of gas in thestrut and hence does not change the characteristics of the spring rateof the gas. Lengthening the strut provides more ground clearance for theengines, thus allowing a more efficient inlet design and less exposureto FOD damage. The shock absorbing and taxi “handling” of the strut arenot affected because the added oil is essentially incompressible and thegas volume (which provides the shock absorbing “spring”) is not changed.

Withdrawing fluid from the strut: Normally, when the aircraft is inflight, the landing gear strut is fully extended by the gas pressureinside the strut, and the oil volume is set to a level that allows fullstroke at landing for absorbing the landing impact. The inventionwithdraws the fluid that had been injected into the strut for on-groundoperations when the aircraft is in a landing configuration, thusrestoring it to “normal” oil content for the landing impact.Accordingly, the touchdown shock absorbing characteristics of the strutare unchanged.

The invention offers the advantage of providing a longer landing gearfor certain operations of the aircraft where that is desirable, withouthaving to pay the cost and weight of a longer landing gear. This isparticularly true with respect to the ability to design a morefuel-efficient engine inlet and reduce costly FOD damage to engines. Inaddition, the invention allows the amount of fluid in the gear to beoptimized for various weight and temperature conditions which may allowfurther weight saving and performance advantages to the aircraft.

These and other advantages will become apparent from the followingdetailed description of a preferred embodiment which, taken inconjunction with the drawings, illustrates by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a landing gear system according to theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a preferred embodiment of the present invention. Theillustrated device provides for the adjustment of the ride height of anaircraft. More particularly, the device allows the landing gear to belengthened or shortened when desired and does so without affecting thespring rate. Additionally, the device may be retrofitted to existingaircraft with minimal effort and cost.

In the embodiment illustrated in the FIGURE, the device of the presentinvention is shown fitted to an aircraft's two main landing gear 12, 14,while the nose gear 16 remains unmodified. Each landing gear includes astrut 18, 20 that includes a piston slidably received within a cylinder.The strut contains both oil as well as a gas and is configured in theconventional manner wherein compression of the piston into the cylindersimultaneously causes the gas to be compressed and the oil to flowthrough restrictive flowpaths. The gas thereby serves as a spring tosupport the load exerted on the strut while the restricted oil flowserves to dampen the movement of the piston within the cylinder.Additionally, the volume of oil within the cylinder determines theoverall length of the strut as the oil is incompressible

In accordance with the present invention, oil may be added to or removedfrom the strut via the lower servicing port 22, 24. Oil from a remotereservoir 30 is pumped into or pumped out of the struts by a pump 26,28. Alternatively, a motor-operated actuator designed to act as asyringe, or any other number of simple means to inject and withdrawfluid can be employed. The pump is controlled by a controller 32 thatmay be configured to receive input from any of a number of sourcesincluding, but not limited to, an Aircraft Data System 34 and AircraftAir/Ground Status indication 36.

The aircraft logic for injecting and withdrawing fluid from the strutcan be simple “air-ground” logic that is commonly available on virtuallyall aircraft. In “ground mode” the system injects fluid into the strutto lengthen it, and in “air mode” the system withdraws the fluid thathad been injected in preparation for landing. Additional sophisticationcan be added to the system to optimize the amount of fluid injected andwithdrawn according to aircraft gross weight and gas temperature so thatoptimum landing gear performance characteristics are achieved over awide variety of operational variables, thus providing additionaladvantages to the landing gear design.

While a particular form of the invention has been described andillustrated, it will be apparent to those skilled in the art thatvarious modifications can be made without departing from the spirit andscope of the invention. Accordingly, it is not intended that theinvention be limited except by the appended claims.

1. A strut for supporting an aircraft while on the ground, comprising: acylinder; a piston slidably received in said cylinder; a compressiblegas contained in said cylinder; an incompressible fluid contained insaid cylinder; and a mechanism for selectively increasing or decreasingthe amount of incompressible fluid in said cylinder from on board saidaircraft to lengthen or shorten said strut.
 2. The strut of claim 1,wherein said mechanism for selectively increasing or decreasing theamount of incompressible fluid in said cylinder comprises a pumpconfigured to pump incompressible fluid between said cylinder and areservoir.
 3. The strut of claim 2, wherein said strut includes a lowerservicing port and said incompressible fluid is introduced into orremoved from said cylinder via said servicing port.
 4. The strut ofclaim 1, further comprising a controller for activating said mechanismas a function of preselected conditions.
 5. A strut for supporting anaircraft while on the ground, comprising: a cylinder; a piston slidablyreceived in said cylinder; a compressible material for supporting saidpiston within said piston subject to a preselected spring rate; amechanism for extending said piston from said cylinder without affectingsaid spring rate.
 6. The strut of claim 5, further comprising anincompressible fluid that is introducible into said cylinder from onboard said aircraft.
 7. The strut of claim 6, further comprising a pumpfor introducing or withdrawing said incompressible fluid from saidcylinder.
 8. The strut of claim 7, wherein said pump configured to pumpsaid incompressible fluid between said cylinder and a reservoir.
 9. Thestrut of claim 8, wherein said pump is activated by a controller thatdetermines when said strut is to be lengthened and when said strut is tobe shortened.
 10. The strut of claim 8, wherein said controller causessaid pump to introduce incompressible fluid into said cylinder when saidaircraft is to taxi in order to achieve a preselected amount of groundclearance.
 11. The strut of claim 8, wherein said controller causes saidpump to remove a preselected quantity of incompressible fluid from saidcylinder prior to landing.
 12. A method of increasing an aircraft's rideheight while on the ground, said aircraft being supported by landinggear with extendible struts, comprising the steps of: disposing areservoir with hydraulic fluid on said aircraft; providing pumps forpumping said hydraulic fluid from said reservoir into said extendiblestruts when increased ride height is desired.
 13. The method of claim12, further comprising the step of plumbing said pump to a lowerservicing port associated with said extendible struts.
 14. The method ofclaim 12, wherein said aircraft has two main landing gear and one nosegear and said pumps are configured for exclusively pumping hydraulicfluid between said reservoir and said main landing gear.
 15. The methodof claim 12, further comprising the step of fitting a controller to saidaircraft for controlling the operation of said pumps.
 16. The method ofclaim 15, wherein said controller determines when and how much fluid isto be transferred between said reservoir and said struts.
 17. The methodof claim 16, wherein said controller causes said pumps to transferhydraulic fluid from said reservoir into said struts while in a “groundmode” and from said struts to said reservoir while in an “air mode.”